Optical,thermal, and structural characterization of the sclerotized skeleton of two antipatharian coral species

Optical, thermal and structural characterization of the skeleton of two black coral species from the Western Caribbean Sea, Antipathes caribbeana and Antipathes pennacea is presented. Optical spectra in the UV–VIS region of both species have a strong absorbance around 350 nm. FTIR spectra in the mid-infrared spectra show the presence of a complex material similar to chitin for both species. X-ray diffraction analyses demanded a deproteinization treatment in order to observe the significant differences in the crystalline structure of chitin. The crystallite size in A. caribbeana is larger than in A. pennacea. Thermal characterization, performed by the photoacoustic technique, shows that in A. caribbeana skeleton the thermal conductivity is higher as compared with the thermal conductivity of the skeleton of A. pennacea. The difference in the thermal properties between coral species could be due to the array and packing of the chitin fiber skeletons.     

Luminescence intensity in coral skeletons from Mona Island in the Caribbean Sea and its link to precipitation and wind speed

This study investigates the potential of using changes of interannual luminescence intensity in hermatypic Montastraea coral skeletons in the northeastern Caribbean as a proxy of precipitation and (trade) wind speed. In order to find wavelength pairs that are well suited to detect variations in the concentration of incorporated terrestrial humic substances in coral skeletons, and thus to reconstruct past run-off and rainfall, three-dimensional excitation-emission matrix fluorescence spectra of seawater samples were investigated on their relationships to local precipitation. Three prominent excitation-emission peaks at 310/430, 425/480 and 390/530 nm were identified. The fluorescence intensities of the wavelength pair 310/430 nm showed a weak relationship, while the wavelength pairs at 425/480 and 390/530 nm showed strong relationships with local precipitation. Variations in luminescence intensities from scans on the coral surface along the growth axis using the wavelengths identified were then compared with instrumental records of regional precipitation and wind speed. In the coral skeleton as well, the wavelength pairs at 425/480 and 390/530 nm were more strongly correlated with regional precipitation and wind speed. This indicates that these two wavelength pairs are well suited to reconstruct past precipitation and wind speed. In order to evaluate the use as a proxy of trade wind variability in the Caribbean, tropical Atlantic region, variations in luminescence intensity were compared with a record of trade wind variability from the southern Caribbean. The two records are strongly correlated, which suggests that luminescence intensity in coral skeletons, at least from Mona Island, can be used as proxy of trade wind variability and precipitation.     

Effects of thermal treatments on the structure of two black coral species chitinous exoskeleton

Black corals (Antipatharians) are colonial cnidarians whose branched tree-like skeleton is constituted of chitin fibrils inside a lipoproteic matrix. The arrangement of the constituents of these materials provides a structure with outstanding physical properties. In this study, the structural properties of black coral skeletons of Antipathes caribbeana and Antipathes pennacea species are explored by means of thermal treatments in the range from room temperature up to 400 °C and the subsequent analysis using X-ray diffraction (XRD), infrared spectroscopy (FTIR), and thermal analysis (DSC/TGA). The effects of thermal treatment from room temperature up to around 210 °C induce the enhancement of the bands in the FTIR spectra and X-ray diffractograms, above that temperature, the FTIR and X-ray peaks become strongly attenuated. These effects are specially observed in the infrared bands associated to chitin at 3298 cm⁻¹ and to the secondary amide stretching around 1663 cm⁻¹, in particular, allowing the identification of the α-chitin in the black coral. XRD shows that the crystallinity index of the black coral chitin at room temperature is 24% and grows when the temperature increases, reaching a maximum value of 37% at 210 °C and decreases for higher temperatures. In addition, DSC and TGA measurements allowed identifying the most important transformation stages during the thermal treatments, namely, evaporation of water and the beginning and progress of degradation, depolymerization, and denaturation processes and finally, the degradation of the main functional groups of coral skeleton and coral chitin, in which the polysaccharide structure of chitin is depolymerized and the protein matrix is denatured.     

Isotropic microscale mechanical properties of coral skeletons

Scleractinian corals are a major source of biogenic calcium carbonate, yet the relationship between their skeletal microstructure and mechanical properties has been scarcely studied. In this work, the skeletons of two coral species: solitary Balanophyllia europaea and colonial Stylophora pistillata, were investigated by nanoindentation. The hardness H_IT and Young''s modulus E_IT were determined from the analysis of several load–depth data on two perpendicular sections of the skeletons: longitudinal (parallel to the main growth axis) and transverse. Within the experimental and statistical uncertainty, the average values of the mechanical parameters are independent on the section''s orientation. The hydration state of the skeletons did not affect the mechanical properties. The measured values, E_IT in the 76–77 GPa range, and H_IT in the 4.9–5.1 GPa range, are close to the ones expected for polycrystalline pure aragonite. Notably, a small difference in H_IT is observed between the species. Different from corals, single-crystal aragonite and the nacreous layer of the seashell Atrina rigida exhibit clearly orientation-dependent mechanical properties. The homogeneous and isotropic mechanical behaviour of the coral skeletons at the microscale is correlated with the microstructure, observed by electron microscopy and atomic force microscopy, and with the X-ray diffraction patterns of the longitudinal and transverse sections.     

Ultrastructural study of the effects of coral skeleton on cultured human gingival fibroblasts in three-dimensional collagen lattices

Natural coral skeleton has recently been introduced as a bone graft substitute which enhances bone formation in man and animals. The effects of NCS on cultured human cells has not previously been investigated. In the present study we report these effects as studied by light microscopy, transmission and scanning electron microscopy in three-dimensional culture. The results showed that natural coral skeleton does not inhibit the normal function of fibroblasts in contracting collagen lattices. After 8 weeks, the cells maintained a healthy ultrastructural morphology. At the collagen/coral interface, the cells were well-spread and attached to the surface by numerous adhesion plaques. Evidence for biosynthetic activity was also observed; the cells showed numerous ribosomes, mitochondria and prominent rough endoplasmic reticulum. Extracellularly, a perigranular dense matrix, appearing as nodules in the SEM, was deposited on the coral surface. This matrix was made of highly organized fibrils lacking periodicity, and a ground substance. The present study shows that coral was well-tolerated by human gingival fibroblasts, and that it provided a surface for cell spreading, attachment and deposition of the special extracellular matrix.     

Photothermal and Structural Comparative Analysis of Chitinous Exoskeletons of Marine Invertebrates

Chitinous materials are common in nature and provide different functions including protection and support of many invertebrate animals. Exoskeletons in these organisms constitute the boundary regulating interaction between the animal and the external environment. For this reason, it is important to study the physical properties of these skeletons, in particular, thermal properties. The objective of this study is to investigate the thermal diffusivity of the skeletons of four species of marine invertebrates, Antipathes caribbeana (black coral), Panulinus argus (lobster), Callinectes sapidus (crab), and Limulus polyphemus (xiphosure). Thermal characterization is performed using photothermal radiometry (PTR) and laser-flash techniques. The measurements are complemented with structural characterization using X-ray diffraction. The results using both laser flash and PTR are consistent. These indicate that the thermal properties are strongly dependent on the presence of biogenic minerals (calcium and/or magnesium) and on the crystallinity index of the structure. The thermal-diffusivity values show an increase as a function of the crystallinity index.     

A model comparison reveals dynamic social information drives the movements of humbug damselfish (Dascyllus aruanus)

Animals make use a range of social information to inform their movement decisions. One common movement rule, found across many different species, is that the probability that an individual moves to an area increases with the number of conspecifics there. However, in many cases, it remains unclear what social cues produce this and other similar movement rules. Here, we investigate what cues are used by damselfish (Dascyllus aruanus) when repeatedly crossing back and forth between two coral patches in an experimental arena. We find that an individual''s decision to move is best predicted by the recent movements of conspecifics either to or from that individual''s current habitat. Rather than actively seeking attachment to a larger group, individuals are instead prioritizing highly local and dynamic information with very limited spatial and temporal ranges. By reanalysing data in which the same species crossed for the first time to a new coral patch, we show that the individuals use static cues in this case. This suggests that these fish alter their information usage according to the structure and familiarity of their environment by using stable information when moving to a novel area and localized dynamic information when moving between familiar areas.     

In situ raman spectral mapping study on the microscale fibers in blue coral (Heliopora coerulea) skeletons

The presence and localization of organic matrix associated with the aragonite phase in the fibers of blue coral Heliopora coerulea skeletons were studied by in situ microRaman mapping spectra, with a spatial resolution of ~0.3 μm. Spatial variations in the amounts and chemical compositions of the fibers were imaged. The results showed that the amide I and the α-helix of amide III were perpendicular to the c-axis of fibers' growth, whereas the β-turns/sheet of amide III was in the parallel conformation. Visible S-S and C-S bonds were consistent with the XANES results, which indicated the existence of organic sulfur in coral skeletons. Regular cyclic changes between aragonite and organic matrix refined a stepping growth mode of the fibers' biomineralization. An inorganic PO(4) bond was detected and exhibited the same concentration variation trends as the v(4) aragonite bands. Instead of providing an ocean P proxy on the subseasonal to centennial scale by LA-ICPMS, the possibility was raised of producing high resolution surface ocean phosphorus records on daily environmental variation via P/Ca variation cycles determined from Raman mapping data.     

Multiphysics modelling of photon,mass and heat transfer in coral microenvironments

Coral reefs are constructed by calcifying coral animals that engage in a symbiosis with dinoflagellate microalgae harboured in their tissue. The symbiosis takes place in the presence of steep and dynamic gradients of light, temperature and chemical species that are affected by the structural and optical properties of the coral and their interaction with incident irradiance and water flow. Microenvironmental analyses have enabled quantification of such gradients and bulk coral tissue and skeleton optical properties, but the multi-layered nature of corals and its implications for the optical, thermal and chemical microenvironment remains to be studied in more detail. Here, we present a multiphysics modelling approach, where three-dimensional Monte Carlo simulations of the light field in a simple coral slab morphology with multiple tissue layers were used as input for modelling the heat dissipation and photosynthetic oxygen production driven by photon absorption. By coupling photon, heat and mass transfer, the model predicts light, temperature and O₂ gradients in the coral tissue and skeleton, under environmental conditions simulating, for example, tissue contraction/expansion, symbiont loss via coral bleaching or different distributions of coral host pigments. The model reveals basic structure–function mechanisms that shape the microenvironment and ecophysiology of the coral symbiosis in response to environmental change.     

Effect of light regimes on the microstructure of the reef-building coral Fungia simplex

We studied the effect of light availability on the skeletal aragonite microstructure of the reef-building coral Fungia simplex. Scanning electron microscopy (SEM) of samples transplanted from light to shade conditions showed that the latter promoted a well-defined crystal alignment and dense packing. An X-ray diffraction (XRD) study of newly formed coral skeleton tissue showed a twofold increase in coherence length along the c-axis under shade conditions, while coherence length along the perpendicular direction remained essentially unchanged. These findings indicate that under shade conditions controlled calcification occurred by extension of the crystalline domains along the c-axis of the prismatic aragonite crystals. The reduced calcification rate under shade conditions was in keeping with the lower algal densities and the higher chlorophyll a content of the zooxanthellae that mediate the calcification process.     

Systematic construction and prediction of the arrangement of the strands of sandwich proteins

The problem of predicting the three-dimensional structure of a protein starting from its amino acid sequence is regarded as one of the most important open problems in biology. Here, we solve aspects of this problem for the so-called sandwich proteins that constitute a large class of proteins consisting of only β-strands arranged in two sheets. A breakthrough for this class of proteins was announced in Kister et al. (Kister et al. 2002 Proc. Natl Acad. Sci. USA 99, 14 137–14 141), in which it was shown that sandwich proteins contain a certain invariant substructure called interlock. It was later noted that approximately 90% of the observed sandwich proteins are canonical, namely they are generated by certain geometrical structures. Here, employing a topological investigation, we prove that interlocks and geometrical structures are the direct consequence of certain biologically motivated fundamental principles. Furthermore, we construct all possible canonical motifs involving 6–10 strands. This construction limits dramatically the number of possible motifs. For example, for sandwich proteins with nine strands, the a priori number of possible canonical motifs exceeds 360 000, whereas our construction yields only 49 geometrical structures and 625 canonical motifs.     

Infrared spectroscopy and X ray diffraction study on the morphological variations of carbonate and phosphate compounds in giant prawn (Macrobrachium rosenbergii) skeletons during its moulting period

A systematic study has been carried out on the quantitative and morphological variations of carbonate and phosphate compounds in giant prawn (Macrobrachium rosenbergii) skeletons during the moulting period on the basis of infrared spectroscopy and X ray diffraction (XRD) analyses. Skeletons samples were prepared from adult giant prawns, extracted from the intact skeletons of the prawns at the ages of 4, 8, 12, 16, 20, 24, 30 days after moulting, as well as from the exuviae skeletons. Their phosphate bands were compared to those of synthetic hydroxyapatite (HAP) and human enamel, while their carbonate bands were compared to those of coral (oculina sp) and sea urchin (psammechinus miliaris) skeletons. It is well known that mineral compounds in human enamel consist mainly of calcium phosphates with a small amount of carbonates, while those found in coral and sea urchin skeletons consist mainly of calcium carbonates, coexisting with significant amount of magnesium. In contrast to those compositions, the spectroscopic data presented in this work display a strong indication that comparable amounts of calcium carbonates and calcium phosphates do exist in giant prawn skeletons during most of their moulting period. Based on the infrared analysis of the carbonate bands it is further suggested that calcium carbonates experience partial conversion from the amorphous to the crystal phase toward the end of the moulting cycle, as confirmed by similar trend exhibited in XRD data. On the other hand, the phosphate bands in giant prawn skeletons were found to be attributed to a mixture of amorphous and microcrystal phases without a clear contribution from apatite phase throughout the moulting period. This is also consistent with the pattern displayed by the XRD profiles. The lack of evidence for the presence of apatites could be understood on the basis of interfering and competing effects induced by the presence of various ions other than calcium phosphate ions, as well as the relatively high susceptibility of calcium phosphates to the associated substitutional effects.     

GENERATING A LAYOUT FROM A DESIGN SKELETON

In the past, researchers have proposed several types of design skeletons from which a human designer can generate good facilities layouts. Examples are flow graphs, SLP space relationships, bubble diagrams, planar adjacency graphs, matching based adjacency graphs, centroid locations, and cut trees. In this paper, we introduce a linear programming model which efficiently generates a layout from a graphical representation of any design skeleton. We demonstrate how the model can be used to enhance most design skeleton based layout approaches.     

Fringe-orientation maps and fringe skeleton extraction by the two-dimensional derivative-sign binary-fringe method

The fringe-orientation information of an interferometric fringe pattern is provided in the form of a fringe-orientation map by spin filtering. The fringe-orientation information is an important feature of fringe patterns and is helpful in many fringe-pattern processing algorithms. With the help of a fringe-orientation map the two-dimensional derivative-sign binary-fringe method is developed to extract fringe skeletons from a fringe pattern with an arbitrary fringe distribution. This fringe skeleton extraction method does not require thresholds and a thinning process. It is relatively robust and highly accurate.     

光纤环及其骨架材料膨胀系数测量方法研究与实现

介绍了一种光纤环及其骨架膨胀系数的简易测量方法,并组建了测量系统。利用铝材和不锈钢,对系统的可行性进行了验证,同时用该系统测量了光纤环及不同骨架的膨胀系数,并对实验数据进行了分析研究,实验结果表明:该系统能够为找出与光纤环相匹配的骨架材料提供技术支撑,具有一定的实用和推广应用价值。     

Natural coral as a substrate for fibroblastic growth in vitro

Coral skeleton is a naturally porous material. This biomaterial is nowadays currently used in humans as a bone graft substitute. Its open porosity provides a large area for potential cell adhesion and for this reason fibroblastic cell proliferation into this material was investigated. McCoy's human fibroblasts were cultured on coral specimens; cell viability and propagation were evaluated by the means of an MTT test and manual counting. Due to the biomaterial porosity, numerous technical adjustments were necessary to ensure an acceptable cell development and evaluation of cell populations. Cell population was evaluated every 3 days over a 24-day period. When compared to cell growth on culture membranes, fibroblasts grew slower on coral during the early time periods, but increased to 2.2 times that of controls from the 12th day after seeding. Natural coral seems to offer a suitable surface for large fibroblastic culture and could be an interesting alternative to synthetic substrates traditionally used for this purpose.     

Multivariate Spartan spatial random field models

This paper introduces a family of stationary multivariate spatial random fields with D scalar components that extend the scalar model of Gibbs random fields with local interactions (i.e., Spartan spatial random fields). We derive permissibility conditions for Spartan multivariate spatial random fields with a specific structure of local interactions. We also present explicit expressions for the respective matrix covariance functions obtained at the limit of infinite spectral cutoff in one, two and three spatial dimensions. Finally, we illustrate the proposed covariance models by means of simulated bivariate time series and two-dimensional random fields.     

The effect of nanoscale surface curvature on the oligomerization of surface-bound proteins

The influence of surface topography on protein conformation and association is used routinely in biological cells to orchestrate and coordinate biomolecular events. In the laboratory, controlling the surface curvature at the nanoscale offers new possibilities for manipulating protein–protein interactions and protein function at surfaces. We have studied the effect of surface curvature on the association of two proteins, α-lactalbumin (α-LA) and β-lactoglobulin (β-LG), which perform their function at the oil–water interface in milk emulsions. To control the surface curvature at the nanoscale, we have used a combination of polystyrene (PS) nanoparticles (NPs) and ultrathin PS films to fabricate chemically pure, hydrophobic surfaces that are highly curved and are stable in aqueous buffer. We have used single-molecule force spectroscopy to measure the contour lengths L_c for α-LA and β-LG adsorbed on highly curved PS surfaces (NP diameters of 27 and 50 nm, capped with a 10 nm thick PS film), and we have compared these values in situ with those measured for the same proteins adsorbed onto flat PS surfaces in the same samples. The L_c distributions for β-LG adsorbed onto a flat PS surface contain monomer and dimer peaks at 60 and 120 nm, respectively, while α-LA contains a large monomer peak near 50 nm and a dimer peak at 100 nm, with a tail extending out to 200 nm, corresponding to higher order oligomers, e.g. trimers and tetramers. When β-LG or α-LA is adsorbed onto the most highly curved surfaces, both monomer peaks are shifted to much smaller values of L_c. Furthermore, for β-LG, the dimer peak is strongly suppressed on the highly curved surface, whereas for α-LA the trimer and tetramer tail is suppressed with no significant change in the dimer peak. For both proteins, the number of higher order oligomers is significantly reduced as the curvature of the underlying surface is increased. These results suggest that the surface curvature provides a new method of manipulating protein–protein interactions and controlling the association of adsorbed proteins, with applications to the development of novel biosensors.     

Secreted,receptor-associated bone morphogenetic protein regulators reduce stochastic noise intrinsic to many extracellular morphogen distributions

Morphogens are secreted molecules that specify cell-fate organization in developing tissues. Patterns of gene expression or signalling immediately downstream of many morphogens such as the bone morphogenetic protein (BMP) decapentaplegic (Dpp) are highly reproducible and robust to perturbations. This contrasts starkly with our expectation of a noisy interpretation that would arise out of the experimentally determined low concentration (approximately picomolar) range of Dpp activity, tight receptor binding and very slow kinetic rates. To investigate mechanisms by which the intrinsic noise can be attenuated in Dpp signalling, we focus on a class of secreted proteins that bind to Dpp in the extracellular environment and play an active role in regulating Dpp/receptor interactions. We developed a stochastic model of Dpp signalling in Drosophila melanogaster and used the model to quantify the extent that stochastic fluctuations would lead to errors in spatial patterning and extended the model to investigate how a surface-associated BMP-binding protein (SBP) such as Crossveinless-2 (Cv-2) may buffer out signalling noise. In the presence of SBPs, fluctuations in the level of ligand-bound receptor can be reduced by more than twofold depending on parameter values for the intermediate transition states. Regulation of receptor–ligand interactions by SBPs may also increase the frequency of stochastic fluctuations providing a separation of timescales between high-frequency receptor equilibration and slower morphogen patterning. High-frequency noise generated by SBP regulation is easily attenuated by the intracellular network creating a system that imitates the performance of a simple low-pass filter common in audio and communication applications. Together, these data indicate that one of the benefits of receptor–ligand regulation by secreted non-receptors may be greater reliability of morphogen patterning mechanisms.     

Mechanisms of size control and polymorphism in viral capsid assembly

We simulate the assembly dynamics of icosahedral capsids from subunits that interconvert between different conformations (or quasi-equivalent states). The simulations identify mechanisms by which subunits form empty capsids with only one morphology but adaptively assemble into different icosahedral morphologies around nanoparticle cargoes with varying sizes, as seen in recent experiments with brome mosaic virus (BMV) capsid proteins. Adaptive cargo encapsidation requires moderate cargo-subunit interaction strengths; stronger interactions frustrate assembly by stabilizing intermediates with incommensurate curvature. We compare simulation results to experiments with cowpea chlorotic mottle virus empty capsids and BMV capsids assembled on functionalized nanoparticles and suggest new cargo encapsidation experiments. Finally, we find that both empty and templated capsids maintain the precise spatial ordering of subunit conformations seen in the crystal structure even if interactions that preserve this arrangement are favored by as little as the thermal energy, consistent with experimental observations that different subunit conformations are highly similar.